There is an urgent need for a vaginal product that will not only protect against sexually transmitted infections but also prevent conception. We propose to further develop such a product, combining the microbicide Carraguard[unreadable], (the main ingredient of which is the sulfated polysaccharide carrageenan) with the synthetic progestin levonorgestrel (LNg). In the previous 5-year period this project was referred to as Project II and we demonstrated the feasibility of Carraguard as a vehicle to deliver LNG into the systemic circulation at doses known to inhibit ovulation. Laboratory studies have shown that Carraguard is highly effective in blocking HIV in vitro. In mice, it has effectively protected against vaginal and rectal infection by herpes simplex virus-2 (HSV-2);it has also prevented human papillomavirus infection in human xenografts. Carraguard is presently being tested for safety and efficacy in preventing HIV transmission in a large Phase 3 trial in South Africa. Its characteristics as a microbicide and its physical properties make the agent an ideal vehicle to deliver a progestin in a microbicide/contraceptive combination. The progestin LNG has a long history of safety when used in various contraceptives and has been approved for clinical use in various delivery systems. The project proposed for renewal includes 1) laboratory studies to optimize the vaginal gel formulation previously tested to allow for future clinical studies of longer duration. The proposed studies will target two modes of contraception. 2) In the first part we shall confirm the efficacy of a high dose of CARRA/LNG (0.75mg/4mL) to delay or prevent ovulation when used "on-demand" before occasional intercourse, and document the modification of cervical mucus as well as sperm motility in the mucus as a second mechanism to prevent fertilization. 3) Another study will explore the consequences on the cycle of too frequent use of the "ondemand" high dose. 4) In the second part, the lowest effective dose of LNG for daily use will be determined (that is, the dose that may modify cervical mucus to prevent sperm penetration without modifying ovulation). 5) Once the effective dose is defined, longer-term use will be tested over three cycles in two different regimens, either daily without interruption or daily on a 21/7 use/non-use schedule to evaluate the approach that will lead to the most acceptable bleeding pattern. Given the scope of the whole project, additional funding will be requested from other sources for the later study as well as for the later phases of formulation development.